Contractors Luis Benitez, foreground, and Jose Diaz clean up lead paint in a contaminated building in Providence, R.I., in 2006. A federal panel recommended Jan. 4 that the threshold for lead poisoning in children be lowered. If new standards are adopted by government officials, 200,000 additional U.S. children could be classified as having lead poisoning.

ATLANTA — For the first time in 20 years, a federal panel is urging the government to lower the threshold for lead poisoning in children.

If adopted, tens of thousands more children could be diagnosed with lead poisoning. Too much lead is harmful to developing brains and can mean a lower IQ.

Recent research persuaded panel members that children could be harmed from lead levels in their blood that are lower than the current standard, officials at the Centers for Disease Control and Prevention said.

While the number of cases has been falling, health officials think as many as 250,000 children have the problem, many of those undiagnosed. The proposed change could take it to 450,000 cases.

The vote recently by the Advisory Committee on Childhood Lead Poisoning Prevention would lower the definition of lead poisoning for young children from 10 micrograms of lead per deciliter of blood to 5 micrograms. The CDC has accepted all of the panel’s recommendations in the past.

Lead — a metal that for years was common in paint and gasoline — can harm a child’s brain, kidneys and other organs. High levels in the blood can cause coma, convulsions and death. Lower levels can reduce intelligence, impair hearing and behavior and cause other problems.

Usually, the victims are children living in old homes that are dilapidated or under renovation, who pick up paint chips or dust and put it in their mouths. Lead has been banned in paint since 1978. Children have also picked up lead poisoning from contaminated soil.

Lead poisoning is detected through a blood test, often when children are toddlers. Most cases are handled by removing the lead source. A special treatment to remove lead and other heavy metals is used for very high levels.

But the problem has seemed to be diminishing, based on the old standard. In 2009, researchers reported that 1.4 percent of young children had elevated lead levels in their blood in 2004, the latest data available. That compares with almost 9 percent in 1988.

The lead poisoning threshold was last changed in 1991.

The new proposed level of 5 micrograms was calculated from the highest lead levels seen in a comprehensive annual U.S. health survey. The panel recommended that it be reassessed every four years.

Some groups celebrated the decision, saying medical evidence has been mounting that lower levels of lead poisoning can erode a child’s ability to learn and can cause behavior problems.

“This is long overdue,” said Ruth Ann Norton, executive director of the Coalition to End Childhood Lead Poisoning, a Baltimore-based organization.

In many places, it’s up to city and county health departments to provide many of the services for lead poisoned kids, and those departments have lost more than 34,000 jobs in the last three years because of budget cuts.